We are delighted to welcome Professor Laura Heyderman to the school as part of our 2024-25 Sir Harrie Massey Colloquia Series.

Professor Heyderman will deliver a lecture titled 'Recent Advances in Artificial Spin Ice'. An abstract and biography can be found below.

Abstract:

Artificial spin ices are metamaterials consisting of coupled nanomagnets arranged in 2D on various lattices with frustrated magnetic configurations. They exhibit interesting emergent phenomena including magnetic monopoles, phase transitions and vertex frustration [1]. The nanomagnets are often made of permalloy and arranged on the square or kagome lattice. The field has now grown tremendously to encompass a large variety of lattices, some aperiodic and some in 3D, each bringing their own fascinating physics.

Artificial spin ices have intriguing phase diagrams, with artificial kagome spin ice predicted to undergo two phase transitions, starting from a paramagnetic phase at high temperature, and eventually reaching a long range ordered phase on lowering the temperature [2, 3]. However, the low temperature phases have never been observed experimentally. By introducing nanoscale bridges between the nanomagnets, the degeneracy of the vertex configurations can be modified. With careful tuning of the bridge widths, we have been able to observe ground state ordering as well as the dynamic magnetic configurations associated with the phase transitions using synchrotron x-ray photoemission electron microscopy [4].

Artificial spin ices are also interesting for nanomagnet-based computation. For example, we have demonstrated a robust nanomagnetic logic in structures based on the artificial square ice, and the possibility to tune the relaxation pathways for probabilistic computing [5]. Lateral chiral coupling in such nanomagnetic systems brings several new opportunities. Here the Dzyaloshinskii–Moriya interaction can be exploited to create strongly coupled artificial spin ices that spontaneously order [6]. Making use of this concept, we have created coupled Ising-like nanomagnets in which the effective coupling between adjacent nanomagnetic regions can be reversibly converted between ferromagnetic and antiferromagnetic using solid-state ionic gating [7]. With this voltage control of the individual coupling, we have realized an electrically programmable Ising network. This opens the way to designing novel nanomagnet-based logic devices and neuromorphic computers.

Extending artificial spin ices to 3D provides a means to explore new geometries and the physics associated with them. We have combined two-photon lithography with deformation-free pyrolysis and a GdCo coating to create a three-dimensional tripod structure that represents a building block of an 3D artificial spin ice. We have mapped the three-dimensional magnetic configuration of the structure and its surroundings using soft x-ray magnetic laminography, which provides useful insights into how a fully extended lattice in 3D will behave [8].

[1]     S.H. Skjærvø et al., Nat. Rev. Phys. 2, 13 (2020)

[2]     G.-W. Chern, P. Mellado & O. Tchernyshyov, Phys. Rev. Lett. 106, 207202 (2011)

[3]     G. Möller & R. Moessner, Phys. Rev. B 80, 140409(R) (2009)

[4]     K. Hofhuis et al., Nat. Phys. 18, 699 (2022)

[5]     H. Arava et al. Nanotechnol. 29, 265205 (2018); Phys. Rev. Appl. 11, 054086 (2019)

[6]     Z. Luo et al. Science 363, 1435 (2019)

[7]     C. Yun et al. Nature Communications 14, 6367 (2023)

[8]     P. Pip et al., APL Mater. 10, 101101 (2022)

Biography:

Laura Heyderman began her career in magnetism in 1988, working on magnetic multilayers as a Bristol University PhD student at CNRS in Paris. As a postdoc using electron microscopy at Glasgow University, she observed magnetic domain configurations in a variety of materials. She then spent four years in industry in the UK and, since 1999, she has been based at the Paul Scherrer Institute. In January 2013, Laura Heyderman became Professor of Mesoscopic Systems at the Department of Materials, ETH Zurich. She is affiliated with the Laboratory for Multiscale Materials Experiments at the Paul Scherrer Institute, where she was Head of Laboratory from 2017 to 2022.

Laura Heyderman’s research concerns the development of lithography methods for the fabrication of structures and devices incorporating sub-micrometre magnets, as well as the development of novel large-scale facility methods for characterising their microscopic behaviour. The large-scale facility characterisation involves mainly synchrotron x-rays, but also low-energy muon spectroscopy and neutron scattering.

An important research focus is artificial spin ice, which is made up of arrays of coupled frustrated magnets arranged on various lattices. These magnetic metamaterials display interesting fundamental phenomena such as emergent magnetic monopoles, chiral dynamics and phase transitions. Laura Heyderman is also interested in the creation and characterisation of three-dimensional magnetic systems, novel magneto-mechanical systems, hybrid systems combining different classes of materials and spintronic devices. These systems provide foundations for next-generation technology including computation, memory, communications, sensors, actuators and micromanipulators.